DIFFERENTIAL MANOMETER

The manometer consists of 3/16" plastic tubing, red Automatic
Transmission Fluid (ATF), about 3 ft. of scrap wood, and a few bits of
bicycle inner tube to hold it together. No calibration is necessary
'cause you're just trying to adjust vacuum to be equal. This setup can
measure about 36" of ATF vacuum difference, or about 2 3/8" equivalent
of Hg vacuum difference. Two cm Hg is supposed to be the maximum vacuum
difference between carbs.

If the cylinders are severely out of whack (> 3" Hg
difference), the ATF will continue to rise and eventually flow into one
carb - quickly pull off the tubes and shut down the engine. Then it
pays to crudely synchronize using a vacuum gauge on each cylinder
before using the manometer.

You can synchronize 2 carbs at a time with the differential
manometer. The other two nipples should be capped.

Turn the engine off to move from one pair of nipples to
another. If you don't, when you remove one tube, the lovely red ATF
will get sucked into the other carb.

GASOLINE TEST TANK

In my case, it's 3/16" tubing stuck into the top of a bicycle
water bottle, with a little hole drilled into the top. To start gas
flow, you cover the hole with a finger, squeeze the bottle 'til gas
fills the tube, then release the hole. To stop gas flow, lower the
bottle below the carbs.

CONSTRUCTION

I used a total of 20' of 3/16" clear tubing, 16' for the manometer, 4'
for the temp gas tank, total investment of about $3 CDN. The ATF was
left over from changing the rear shock fluid.

The good thing about the 3/16" tubing is that it fits over the
Concours vacuum nipples and press-fits into the 5/16" gas line to the
carbs.

I know this works, it's extremely accurate, and it's frugal,
which rests well with my Scottish blood.